1. Field of the Invention
The present invention relates to a composite microwave circuit module assembly, and more particularly to a composite microwave circuit module used for microwave communication apparatuses and to a connection structure for connecting such a microwave circuit module to a module of the same configuration or other external circuitry.
2. Description of the Related Art
In a prior art microwave circuit module, as shown in FIG. 1, a circuit substrate 10, which comprises a film conductor formed on a dielectric substrate of alumina ceramics or the like, is disposed on each lateral side of an active element 11 for connecting the active element with a small interval therebetween. That is, the prior art microwave circuit module has a plurality of circuit substrates 10. Further, the module has many connection lines such as wire bondings 12 for the connection of these circuit substrates 10. A single-layer parallel-plate capacitor 13 acting as a coupling capacitor is mounted on the circuit substrate 10 and connected by means of wire bonding. Further, a resistor element is formed as a thin film of tantalum nitride or the like only on the surface of the circuit substrate 10. Further, to protect the active elements from the outside, a metal cap 14 is completely bonded to a case base (generally referred to as "header") 15 by means of resistance welding. The metal cap 15 also serves the role of a shield to prevent leakage of radio-frequency (RF) signals to the outside.
As described above, the prior art microwave circuit module requires a plurality of circuit substrates 10 and components such as single-layer parallel-plate capacitors 13, which have been presenting problems in promoting the structural simplification and size reduction in a mounting structure. In addition, an increased number of points of connection of many components has led to deterioration of the RF characteristics and has required a large number of assembling steps, thus making it difficult to reduce manufacturing cost.
In recent years, Microwave Monolithic Integrated Circuit (hereinafter referred to as "MMIC") are finding practical applications. Even the MMIC, however, has limitations imposed on its applications. The MMIC is usually formed on a Si (silicon) or GaAs (gallium arsenide) wafer by using semiconductor manufacture techniques based on the photolithographic technology. Although lumped constant circuit elements such as transistors and diodes which are active elements are small in scale, distributed constant circuit elements such as directional couplers and filters which are passive elements are large in scale and pose problems when assembling them in the MMIC. Large scale chips are disadvantageous in view of the yield of manufacture and cost. Therefore, conventional MMIC chips have not included therein large scale passive circuit elements as noted above.
Since the MMIC is unsuited for the assembling of the passive circuit elements, in the prior art microwave circuit, the active elements are accommodated in a small size air-tight sealing case while constructing the remaining connection lines and the passive circuit elements with microstrip lines, and these components are connected to one another by means of soldering. For shielding such components and connection lines from external circuits, a complicated and expensive shield case with a plurality of small chambers formed by partitioning is necessary.
The prior art connection structure is applicable to modules of the type in which only active elements are accommodated and lead terminals thereof project for soldering.
However, there is a demand for compact composite microwave circuit modules which also accommodate passive elements. Since passive elements are large in scale, the provision of such elements in the module increases the module area or dimension and manufacturing cost.
With the prior art structure of connecting together composite microwave circuit modules by soldering, it has not been possible to make an effective reduction in the number of processing steps and an effective improvement in the stability of the radio frequency connection performance.